<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            background-color: #bbb;
        }

        #canvas {
            background-color: #fff;
        }
    </style>
</head>

<body>
    <canvas id="canvas" width="400" height="400"></canvas>
</body>
<script src="./utils.js"></script>
<script>
    window.onload = () => {
        var canvas = document.getElementById("canvas")
        var context = canvas.getContext('2d')
        var pt1 = { x: 100, y: 100 }
        var pt2 = { x: 200, y: 200 }
        var c1 = { x: 150, y: 150, radius: 0 }
        var c2 = { x: 150, y: 150, radius: 50 }
        gradient = context.createLinearGradient(c1.x, c1.y, c1.radius, c2.x, c2.y, c2.radius)

        gradient.addColorStop(0, "#000000")
        gradient.addColorStop(1, "rgba(0,0,0,0)")

        context.fillStyle = gradient
        context.fillRect(100, 100, 200, 200)
    }
</script>

</html>